Pbocess of nitbamng hedbocabbong



Jill 2, 1940.

H, B. HASS'EIAL PROCESS OF NITRATING HYDROCARBONS Filed Aug. 31, 1936Recieuer Patented J l a UNITED S- success or Aren't mo rrirmiooannoxsporation of Indiana Application August a1, 1936, Serial No. 98.63;Claims. (cl. zoo-s44) Our invention relates to the nitration ofsaturated aliphatic hydrocarbons, and more particularly to the nitrationof saturated hydrocarbons of the paraflin series having" in excess oftwo car- 5 bon atoms, by means of nitrogen dioxide.

Numerous efforts have been made in the past to develop a satisfactorymethod of obtaining nitro derivatives of the saturated hydrocarbons.vRegardless of availability and cheapness of the latter, however, nopractical commercial process has been developed prior to that disclosedin United States Patent No. 1,967,667, of July 24, 1934, granted to uswith Byron M. Vanderbilt as co-inventor. According to that process,saturated aliphatic hydrocarbons having from three to eight carbonatoms, and especially those having secondary or tertiary carbon atoms,are nitrated in the gaseous or vapor phase by the aid of vapors obtainedby heating nitric acid, which contain nitrogen dioxide mixed with othersubstances.

We have now found that we may also obtain eflective vapor phasenitration of hydrocarbons higher than those having eight carbon atoms,such as decane, eicosane, triacontane, or paraflln wax, which is amixture of a number of high molecular weight hydrocarbons.

We have also found that saturated aliphatic hydrocarbons may be moresatisfactorily nitrated by substantially pure nitrogen dioxide in placeof the vapors formed by heating nitric acid. The use of substantiallypure nitrogen dioxide permits improvements in operating procedure whichwill be apparent from the description of our improved process whichfollows. Among such improvements are these: By using substantially purenitrogen dioxide we can obtain more nearly optimum yields, over a widertemperature range, and thus eliminate the necessity for such precisetemperature control as is necessary for obtaining such optimum yields,at any given space velocity when vapors of nitric acid are used. Also,by using nitrogen dioxide substantially free from water and nitric acid,we facilitate operation M under pressure, lessen condensation, obtain amore selective nitrating action on secondary and tertiary carbon atoms,and obtain greater economy in the recovery of the nitrating agent used.

Our process may be illustrated by reference to the figure, which shows alaboratory apparatus suitable for the application of our process. In

the apparatus shown in the diagram, carbon dioxide, or other inert gas,passes through the pipe J, the rate of flow of the inert gas beingregulated 55 by the aid of the flow-meter F. The carbon dioxide bubblesthrough liquid nitrogen dioxide in the cylinder A, the temperature ofwhich is regulated by the bath B maintained slightly below the boilingpoint of the nitrogen dioxide. By reguco lating the flow of carbondiomde through the liquid nitrogen, dioidde the proportion of gaseousnitrogen dioxide to hydrocarbon in the reaction mixture may be changedas desired. It is to be understood, however, that other suitable methodsof regulating the proportion of nitrogen dioxide to hydrocarbon may beemployed without departing from the scope of our invention. Incommercial scale operations, for example, the carbon dioxide, or otherinert gas, may be dispensed with, if desired, and the gaseous or liquidnitrogen dioxide pumped into the system at determined rates in order togive the desired proportion of reactants.

The hydrocarbon to be nitrated enters the system in a gaseous statethrough the pipe K, the amount of gas admitted being regulated by theaid of the flowmeter F, or other suitable means. The gaseous reactantsmeet at L and pass through the coil R maintained at the reactiontemperature. This may be accomplished by any suitable means permittingsatisfactory temperature control, such as, for example, by the use ofelectrical heating coils, a molten lead bath or a bath of the molteneutectic mixture of sodium nitrite and potassium nitrate, a bath of thislatter type being represented as C in the drawing.

The gaseous reaction products pass through a condenser D where part ofthe nitrated product is condensed and collected in the receiver E,preferably surrounded by an ice bath G. The uncondensed gases are thenpreferably conducted to an auxiliary condenser H, cooled by a solidcarbon dioxide bath I, or a refrigerating coil, which serves to removethe greater part if not all of the remainder of the nitroparafiins and asubstantial portion of any nitrogen dioxide and hydrocarbon remaining inthe gaseous reaction mixture. The uncondensed gases leave the system atM and. consist mainly of unreacted hydrocarbon together with smallerproportions of carbon dioxide, carbon monoxide, nitric oxide, andnitrogen dioxide. Obviously,'however, the composition of the gaseousby-products depends to a large extent upon the particular reactantsemployed and whether or not an inert diluent gas is used to regulate theadmixture of the nitrogen dioxide with the hydrocarbon being nitrated.

The operation of our process will be specifically illustrated by thenitration of isobutane. Carbon dioxide gas, at the rate of two litersper hour, was passed through the cylinder of nitrogen dioxide A,maintained at approximately 18 C. At the same time gaseous isobutane waspassed through the flowmeter F, at a rate of fifty liters per hour. Thetwo gaseous reactants after mixing at L were passed through the coil Rof 17 ml. capacity, maintained in a NaNOz-KNO: salt bath kept at atemperature of 420 C. The exit gases were cooled in the water cooledcondenser D and then passed through the receiver E, and the auxiliarycondenser H which was cooled by solid carbon dioxide, and the nitratedproducts were collected in both vessels E and H. The nitrated productthus obtained represented 41% of the theoretical conversion of thenitrogen dioxide to.

nitro compounds.

The procedure outlined above for the nitration of isobutane isapplicable to other saturated nonbenzenoid hydrocarbons having more thantwo carbon atoms, such as, for example, propane, n-butane, pentane,hexane, heptane, octane, decane, eicosane, triacontane, cyclohexane,decahydronaphthalene, etc., as well as mixtures of hydrocarbons, such,for example, as paraflin wax. With the different hydrocarbons, however,the rate of reaction varies somewhat, and hence in order to obtain thebest results in any particular case it is usually necessary to vary tosome extent the temperature of reaction, the proportion of thereactants, and the space velocity of the reaction mixture. These slightvariations in operating conditions, however, ordinarily present noparticular difiiculties. When, for example, it isv desired to operate-atsome particular temperature the space velocity of the reaction mixturemay be regulated by observing the gases from the reaction vessel andadjusting the space velocity so acterot the hydrocarbon, determine theexact ratios below which it is impractical to go on account of danger ofexplosions. On the other hand, increasing the ratio of hydrocarbon tonitrogen dioxide increases the conversion of the nitrogen dioxide tonitro compounds. The cost of handling and recirculating large excessesof hydrocarbon limits 'from a practical and economical point of view-theupper limits of the ratio of hydrocarbon to nitrogen dioxide. In thecase of isobutane, a practical ratio for -most purposes appears to be ofthe order of 4 6 mol parts'of hydrocarbon to 1 mol part of nitrogendioxide. As the molecular weight of the hydrocarbon increases, themolecular ratio of hydrocarbon to nitrogen dioxide may be decreased.

The temperature may be varied through a fairly wide range withoutgreatly affecting the degree of conversion, although it is necessary tovary the space velocity to compensate for temperature changes.Temperatures ranging from 300 C. to 600 C. may in general be employed.For most purposes a temperature of theorder of 475 C. is satisfactory.

The data shown in the following table will illustrate the resultsobtained by our process when carried out according to the example setforth that the brown color characteristic of nitrogen above.

Table i halrinountbof Al nlglnt Rate of Partial T lSuace velocity, Conyrocar on o a, pressure emperaere reac an s version, Hydrocarbon weightin weight in figgg of reacture, C. per liter space percent grams gramstants per hour N O:

at 13. e 2 0. 908 420 3, 530 is 66 15, 0 2 0. 968 475 3, 580 17 40. 415. 4 3. 4 0. 971 515 14, 400 12 40. 4 14. 1 3. 6 0. 970 550 14, 18

97. 2 16. 4 2 0. 968 420 3, 560 44 l 86. 4 13. 8 .2 D. 968 480 3, 530 25129. 7 15. 4 8 O. 967 450 13, 530 36 86. 4 2i. 2 2 0. 971 540 8, 360 29.2 64. 8 14. l 4 0. 971 7 540 15, 940 39. 2 108. 1 18 9 4 0. 968 525 15,280 39. 4

dioxide is no longer, or only barely, visible therein. By way ofexample, if an operating temperature of 475 C. is selected, the spacevelocity for the reaction mixture used in the isobutane exampledescribed above may be variedbetween 3000 and 20,000, the preferredrange, however, being between 8000 and 15,000.

The proportion of hydrocarbon to nitrogen dioxide may be varied withinfairly wide limits. By decreasing the proportion of hydrocarbon tonitrogen dioxide the conversion of the hydrocarbon is increased. Thisproportion of hydrocarbon, however, should not be lowered suflicientlyto approach too closely an explosive mixture. The presence or absence ofinert gases and the character and amount of same, as well as the char-As has previously been pointed out, our invention is applicable to thevapor phase nitration of liquid or normally solid hydrocarbons as wellas gaseous hydrocarbons. For example, nitrations of decane and cetanewere efiected in an apparatus similar to that shown in Figure 1 with theexception that the flow-meter F was omitted, the rate of flow of thehydrocarbon being controlled in the liquid state; a vaporizer for thehydrocarbons was inserted in the bath C preceding the reaction coil R;and the COz-NOz mixture was introduced into the reaction coil R in theform of a jet, simultaneously with the vaporized hydrocarbon. The datashown in Table II illustrate the results obtained when operatingaccording to this procedure.

Table II I Amount of Amount Partial Space velocity, hydrocarbon of N0Rate of pressure Temperaliters reactants Comer Hydrocarbon flow of 00sion erweight in weight in of reacture, C. or liter s ace p gramsliters/hr. tan 9 per cent N0;

DQ011118 158 9 5. 5 0. 891 330 472 Z; Octane 36 8. 2 5. 5 0. 846 320 31725 The vapor phase nitration of normally solid hydrocarbons may beillustrated by the nitration of parafin wax in which case an apparatussimilar to that employed in the nitration of the liqdid hydrocarbons inthe preceding example was used, with the exception that all of thehydrocarbon was placed in the vaporizer and a stream of carbon dioxidewas passed through the molten Wax, the rate of hydrocarbon feed beingcontrolled by the rate of carbon dioxide flow. Nitrations were effectedunder the operating conditions shown in Iable 111.

ess will naturally occur to those skilled in the art. It is to beunderstood that any such modifications or the use of any equivalentswhich would naturally occur to those skilled in the art are includedwithin the scope of our invention.

It is to be understood, also. that with respect to the nitration ofhydrocarbons having more than eight carbon atoms we do not limitourselves to the use of substantially pure nitrogen dioxide as thenitrating agent, but may also use less pure materials such as nitrogendioxide obtained by thermal decomposition of nitric acid, in which TableIII Amount Rate of Rate of Space velocity of'hydro- 3 33 flow of CO1flow oi CO; gigg Tem liters reactant-s Hydrocarbon carbofiit, weigh?tlgxoggh h iglmuglg P of s per litelil space weig 1 y rocar on per ourin grams m grams liters/hr. liters/hr. acmnts lamfiin wax..- 155 29. 53. 2 8. 6 0.636 375-400 217 Do i 50 I 41 1. 2 32 0. 800 300-335 150Conversions were not calculated for these nitrations in view of theunknown molecular composition of the original hydrocarbon mixture and ofthe products, but in both cases satisfactory nitrations were secured asevidenced by complete utilization of the N02 and isolation of nitrocompounds in the products.

It is to be understood, of course, that our invention is not to beconstrued as limited to .the particular procedures set forth in theabove examples. Numerous modifications of the process will naturallyoccur to those'skilled in the art. For example, the process may beoperated in a cyclic manner if desired. The exit gases from thecondensation and scrubbing systems contain nitrogen oxides, carbonmonoxide, carbon dioxide, water vapor, nitroparafiins and hydrocarbons,the amounts and proportions of which vary wide- 1y with the particularhydrocarbon being nitrated, the proportion of reactants used, and thecharacter of the recovery system. In the case 01 low boilinghydrocarbons such as, for example, propane and isobutane, the greaterportion of the unreacted hydrocarbon may remain in the exit gases afterthe condensation of the nitroparaflins. In such cases, additionalhydrocarbon and nitrogen dioxide may be added to give a gas mixture ofsubstantially the original composition, which may then be recirculatedthrough the reaction system. 7

Likewise, if desired, the exit gases may be compressed sufiiciently topermit the separation of unconverted hydrocarbon from the nitric oxide,carbon monoxide, etc., and the nitric oxide'then reconverted to nitrogendioxide. The entire nitration operation may even be carried out undersufliciently elevated pressures to cause liquefaction of the unconvertedhydrocarbon in the receiver along with the nitroparafllns. It mayalsobeconducted under reduced pressure, which is often desirable in the caseof higher boiling hydrocarbons. Numerous other modifications of ourproccase the nitrogen dioxide need not be separated from anyundecomposed nitric acid.

Now having described our invention, what we claim is:

1. A process for the production of nitrohydrocarbons which compriseschemically combining, by contacting wholly in the vapor phase,substantially pure nitrogen dioxide and a saturated hy drocarboncontaining more than two carbon atoms, at a temperature of 300 to 600 C.

2. A process for the production of nitrohydrocarbons which compriseschemically combining, by contacting wholly in the vapor phase,substantially pure nitrogen dioxide and a saturated hyiii drocarboncontaining more than two carbon atoms, at a temperature of approximately475 C.

3. The continuous process of nitrating saturated hydrocarbons .having inexcess of two carbon atoms, which comprises passing a mixture ofsubstantially pure nitrogen dioxide and a saturated hydrocarbon througha reaction vessel maintained at a temperature between 300 and 600 0.,and regulating the space velocity of the reactants so that thecharacteristic brown color of nitrogen dioxide is practically invisiblein the gaseous reaction products.

4. A continuous process for the production of nltrohydrocarbons whichcomprises chemically combining, by contacting wholly in the vapor phase,substantially pure nitrogen dioidde and a saturated hydrocarboncontaining more than two carbon atoms, at a temperature of 300 to 600C., and at a space velocity of 3,000 to 20,000.

5. A process of nitrating a saturated aliphatic hydrocarbon having morethan 2 carbon atoms, which comprises producing contact between andchemically combining such saturated aliphatic hydrocarbon andsubstantially purenitrogen d1- oxlde, with both reagents wholly in thegas or vapor phase.

I HENRY B. BASS.

EDWARD 2B. HODGE.

